(1) Field of the Invention
The present invention relates to a novel .alpha.-methylcinnamic acid ester derivative, which is valuable as a ferroelectric liquid crystal or an additive to a ferroelectric liquid crystal. Moreover, the present invention relates to a ferroelectric liquid crystal composition comprising this methylcinnamic acid ester derivative.
(2) Description of the Related Art
The mesophase of the liquid crystals widely used in a light-receiving type display at the present belongs to the nematic phase. Therefore, the display is characterized in that it does not fatigue the eyes and consumes very little energy. However, this type of display has problems in that the response speed is low and the display cannot be seen from a certain angle.
A display device or printer head using a ferroelectric liquid crystal having a much higher response speed and contrast than those of a nematic liquid crystal has been investigated.
The ferroelectric liquid crystal was discovered for the first time by R. B. Meyer et al in 1975 [J. Physique, 36, L-69-71 (1975)]. This ferroelectric liquid crystal belongs to the chiral smectic C phase (hereinafter referred to as "Sm*C phase" for brevity), and a typical compound of this ferroelectric liquid crystal is p-decyloxybenzylidene-p'-amino-2-methylbutyl cinnamate (hereinafter referred to as "DOBAMBC" for brevity) represented by the following formula (2): ##STR4##
As well as DOBMBC, the ferroelectric liquid crystal materials prepared until now have an azomethine bond and a --CH.dbd.CH-- group in the molecule, and thus are readily hydrolyzed and photoisomerized.
In addition to these problems, the liquid crystal with an azomethine bond in the molecule has another problem in that a good image quality of the display cannot be obtained because of undesirable coloration. Moreover, the temperature range showing ferroelectric characteristics (the temperature range where the Sm*C phase is present) is narrow, and therefore, trials have been made to expand the temperature range showing the Sm*C phase to the lower and higher temperature sides with room temperature being as the center by mixing several ferroelectric liquid crystals. However, these materials are still not satisfactory in that the temperature showing the ferroelectric characteristics (the temperature at which the Sm*C phase is present) is higher than room temperature, and therefore, a practical utilization of these materials is difficult. Accordingly, development of a ferroelectric liquid crystal having the Sm*C phase present in a practical temperature range is desired. Moreover, a ferroelectric crystal having a larger spontaneous polarization than that of the heretofore developed ferroelectric liquid crystals is desired as a liquid crystal for a printer head for which an ultra-high response speed is required.